The present invention relates to a warehouse system and particularly to apparatus for automatically transferring articles to and from the system.
With the ever-increasing demands for moving articles, in commerce, it has become necessary to increase the through-put capacity of warehousing systems so as to efficiently store and retrieve such articles at these facilities which provide retail and other outlets with a variety of different items. In recent years, the use of semi-automated equipment in place of manual transferring equipment has been incorporated with limited success in an attempt to increase the efficiency of warehousing systems. More recently, stacker cranes have been developed which travel down aisles of multi-tiered storage bins. These cranes are guided by an operator who locates the stacker crane across from a desired storage location and then either manually picks from that storage location or can extend lifting forks or the like into the storage bin to store or retrieve articles therefrom. In the more sophisticated systems, the operator is replaced by some type of electronically operated control system.
Even more recently, a system has been developed that is described in U.S. Pat. No. 3,503,530, Arthur R. Burch, et al., issued Mar. 31, 1970 and which employs a first vehicle which travels across the aisles of the storage rack on tracks and carries with it a second vehicle which can be dispatched down the aisles. The second vehicle includes a mobile vertical elevator for aligning a picking unit with a storage bin. The picking unit then can retrieve or discharge articles between the storage bin and the second vehicle. The first vehicle includes a load station for transferring the articles between the second vehicle and first vehicles.
Although such a system represents an improvement in efficiency over manual picking systems, this system as well as the semi-automatic stacker crane systems lacks the through-put capacity since the vehicle which travels in the aisle is adapted to move vertically as well as along the aisle and therefore, only one vehicle can be employed for each aisle end. Thus, the maximum numbers of vehicles that actually store and retrieve articles into and out of the system is limited to two for each multi-level aisle assuming that each end of the aisle has a first vehicle that can transfer an associated second vehicle from aisle to aisle. In many warehouses only one aisle end is available thereby limiting vehicles which accomplish the transfer of articles to and from the storage bin to one per aisle.
The use of a stacker crane or other systems which have the ability to travel the length of one aisle and elevate within the aisle to any of the storage bin heights requires that a single unit have enough through-put capacity to handle the through-put required for each aisle. Because of the input and output systems usually associated at one end of the system, it is not feasible to operate two such stacker cranes in one aisle. This provides, in some cases, a significant limitation to the through-put capacity of the system which is best suited for extremely long aisles of storage. If long aisles are employed, however, the throughput is limited by the efficiency of the operation of the stacker crane. On the other hand, if the storage location is laid out to include many short aisles to overcome this limitation, a plurality of the relatively expensive stacker cranes or their equivalent are necessary to obtain the desired through-put. The expense of the system rises significantly, since each vehicle is relatively complex to provide along-the-asile movement as well as vertical movement in addition to the picking motion required to reach into a storage bin. Thus, these systems have undesirable limitations either as to efficiency in their ability to provide the desired through-put or as to their expense if employed with shorter aisles to provide the desired through-put capacity.
Another important limitation upon existing systems of this type is the fact they require the entire aisle to be unobstructed vertically. This is considered a serious fire hazard and places a limit on the height to which articles may be stored. This invention eliminates this problem because no or only limited vertical movement of the articles is performed in the aisles.